Magnetohydrodynamic generators



3,278,798 MAGNETOHYDRODYNAMIC GENERATORS Jean Fabre and Zicu Croitoru,Paris, France, assignors to Electricite de France (Service National),Paris, France Filed Mar. 25, 1964, Ser. No. 354,679 Claims priority,application France, Apr. 1, 1963,

3 claims. (cl. 315-411) The present' inyention relates to methods anddevices for producing a strongly ionized gaseous stream and inparticular an ionized gaseous stream intended to produce availableelectric current in a generator of the magnetohydrodynamic type.

The chief object of the 'present inventionfis 'to improve t theefficiency and uniformity of ionization in a magnetohydrodynamicgenerator.

The invention is concerned with a method of producing onincreasing theionization of a gaseous stream, by the application of a succession ofluminescent discharges or arcs, of relatively short duration in severallocalized zonesof said gaseousstream.

For producing or increasing the ionization of a gaseous` stream flowingthrough a conduit of a magnetohydrodynamic generator, we provide in saidconduit, in lcombination, a series of pairs of ionization electrodescarried by the walls of said conduit and disposed in such manner thatthe discharge ends of every pair are located opposite each other insidesaid conduit in said gaseous stream, and means for applying between thefeed ends of every pair, which are disposed outside lsaid conduit,voltage pulses, having `a sutficient amplitude to start discharges orarcs between the corresponding discharge ends.

'In a preferred embodirncnt the ionization'electrodes are disposed insuch manner that the straight lines defined by the couples of dischargeends of every pair of said lelectrodes are substantially parallel to thedirection ofl the magnetic field, generally provided in amagnetohydrodynamic generator, thereby providing for a given quantity ofionizing energy, a higher degree of ionization than when these straightlines make a substantial angle with said direction. Preferredembodiments of our invention will be hereinafter'described withreference to the appended drawings, given merely by way of example, andin which: FIG. 1 diagrammatically shows in perspective view anembo'diment of a conduit, belonging to a magnetohydrodynamic generator,through which flows a gaseous stream, this conduit being-made accordingto our invention;

FIG. 2fis a view similar toFIG. 1 corresponding to another embodiment ofthe invention; A

FIG. 3 shows an example of means for applying voltage pulses.

In FIGS. 1 and2, itflwill be supposed that a gaseous,

preferably hot, stream F fiows at high speedthrough a conduit 1 (forinstance of square or rectangular cross section) made of an insulatingmaterial (for instance glass). This conduit belongs to amagnetohydrodynamic generator and is located in a substantially uniformmagnetic field A 'H (for instance'pcrpendicular to the side walls 2 ofconduit 1). T his conduit carries a series of pairs of collectingelectrodes 3, 4 for collecting positive and negative electric charges,these electrodes being disposed with their v i faces parallel to themagnetic' field H and lto the direction 3118398 Patented Oct. `1 1, 1966'ice . of the gaseous stream F, for instance on the side walls 5 ofconduit 1. The electric voltage thus created is to be used in loadresistors 10 shown in FIG. l, but not shown, i

in FIG. 2 in order to simplify it.

According to the present invention, ionization of gas- ,V eous stream Fas it flows in conduit 1 is obtained or increased by producing aseries'of luminescent discharges or arcs, of relatively shortduration,in several localized zones of said gaseous stream (conduit 1).

The discharges or arcs ionize the gaseous stream inside conduit 1 byproducing on the one hand negative electrons and 'on the other handpositive ions. These electrons and ions diifuse through :the fluidstream and .tend to bedistributed therein in a substantially uniformmanner if said localized zones are sufficiently close to one another.After some milliseconds, the negative electrons and -the positive ionsrecombine; however if the discharges or arcs are sufficiently frequent(for instance if .the frequency of repetition is higher than 1000 cyclesper second), it is possible to obtain a substantially statisticequilibrium, thelnumber of on-electron pairs in a given volume remainingsubstantially constant inside a given volume, duringlthe operation ofgenerator.

Furthermore, if the gaseous stream contains an easily ionizablesubstance, in particular an alkaline metal` such as cesium, in thepowdery or vapor state fortinstance, the discharges or arcs ionize notonly the gas of the gaseous stream but also said substance, therebyproducing or increasing the ionizatio'n of the whole body of the gaseousstream with a satisfac-tory efficiency.

VAccording to the present invention, said ares' are produced by means ofvoltage'pulses having a sufficient ampli-.

tude to produce discharges or arcs' between the discharge ends 6a, 7a,or 8a, 9a of a series of pairs of vionization electrodes 6, 7`(FIGURE l)or 8, 9't`FIGURE' 2) whichV are distinct from the collecting electrodes3, 4 andcarried 1,

by the side walls S (in the embodiment of FIGURE 1) or 2 (in theembodiment of FIGURE 2) of co'ndui',V 1. Said discharge ends of everypair of ionization electrodes are located opposite each other in thegaseous stream inside conduit l. Said voltage pulses are applied (meansnot shown) between every pair 'of input ends 6h, 711, or 8b, 9b locatedoutside conduit 1.

The distance between the ionization electrodes of every pair isadvantageously substantially equal to the distance between the walls.ofconduit 1 that carry said electrodes, whereby these clcctrodes do notprotrude substantially inside conduit 1. If these electrodes protrudedsubstantially they would be eroded by the generally hot gas flowingthrough said conduit. v

Thefrequency of repetition of the arcsis chosen in accordance with'thespeed of recombination of ions and electrons. It may for instanceaverage 1000 cycles-` per second.

Preferably, as illustrated in FIG. 2, the ionization electrodes 8 and 9are disposed in 'such manner that the straight lines defined 'by -thecouple of discharge ends 8a,

9a of every pair are` substantially parallel to the dir-'ecv tion oflthe `rlnagnetic'field H, thereby yproducingrfor a given ionizingenergy, a more intensive 'ionization than when these lines make asubstantial angle with said'direction, because the passage of theionizing electric cur- V rent is easier in av direction parallel 'to themagnetic lfield than transversely to said direction. v

'pair agravos 'known per se, illustrated in FIG. 3. Such a devicecomprises:

(a) a first circuit, or charging circuit, consisting of a high voltagesource 11 (advantageously common to all the circu'its for the differentpairs of ionization electrodes) a capacitor 12 and a resistor 13,capacitor 12 being gradually charged by source 11 through resistor 13during a first phase; and i (b) a second circuit, or discharge circuit,comprising, in addition to capacitor 12, a spark gap 14, this secondcircuit serving to feed the ends 6b, 7h or 8h, 9h of a of ionizationelectrodes 6, 7, or 8, 9, respectively. The ionized gaseous stream thatflows between the discharge ends 6a, 7a or 8a, 9a of the electrodescloses the electric circuit between these discharge ends. When capacitor12 has been charged, at the end of the first phase of operation, to asufliciently high potential difference, a spark is produced in spark gap14 and a discharge takes place between the ends 6a, 7a or 8a, 9a. Thisis the second phase of operation, which constitutes, with the firstphase, a cycle of operation of the device.

IA new cycle (charging of capacitor 12 by the first circuit anddischarging of said capacitor 12 by the second circuit with prodution ofdischarges at 6a, 7a or 8a, 9a) starts then again and so on, thecapacitance C of capacitor 12 determining the duration of the dischargesin the gaseous stream between the ionization electrodes, whereas theproduct CR (R being the resistance of resistor 13) determines thefrequency of the discharges.

If it is' desired to obtain an ionization which is substantially uniformin space and in time inside conduit 1, i.e., a constant density ofionization in each mall volume of the fluid stream during operation,then the successive pairs of ionization electrodes should be locatedsnfficiently close to one another and the voltage pulses should beproduced with a frequency of repetition suiciently great -to obtain asubstantially homogeneous and constant sta- `tistic distribution of theelectrons and of the ions inside the conduit during operation.

It is thus possible to bring the electric conductivity of a gaseousstream intended to supply electric current in a magnetohydrodynamicmachine (said stream consisting for instance of argon with 0.l% ofpotassium, under atmospheric pressure at a temperature of 2000 K.) to avalue ranging from about ten to several hundreds of mhos per meter, forinstance equal to about fifty mhos per meter. p

ATheI present invention permits the production or increase of theionization of a gaseous stream.

We may also apply the invention to varying the mean conductivity of agaseous stream. In order to obtain such a variation, the frequency ofrepetition of the discharges of arcs is varied by varying the frequencyof repetition of the voltage pulses applied to the feed or input ends6h, 7b or Sb, 9b of the ionization electrodes 6, 7 or '8, 9.

It is even possible to modulate the mean conductivity of a gaseousstream, by modulating the frequency of repetition of the discharges orarcs.

The present invention has, over prior methods and devices, manyadvantages in particular as follows:

First it permits the ionization of a gaseous stream in a simple andefiicient manner.

It permits the varying of the conductivity of a gaseous stream byvarying the degree of ionization.

The ionization method and =means according to the present invention aretherefore quite different from the prior methods and means, inparticular from that disclosed in the U.S..Patent No. 3.080,515 issuedonMarch 5, 1963, to Edward Charles Kehoe according to which there iscreated, by means of a single arc, a single conductor localized at agiven time and which is displaced along a conduit. VOn the contrary,according to the present invention, we produce an ionization distributedin the whole volume of gas, in particular in the whole of the conduit1.of a magnetohydrodynamic generator.

It follows that, in the method and device disclosed by said U.S. PatentNo. 3,0S0,5l5, the electrodynamic forces are exterted on a thin slice ofgas whereas, according to the present invention, the electrodynamicforces are distributed throughout the gaseous volume, in particularconduit 1. As a consequence, for a given flow rate and for a givenextracted power, the length of a magnetohydrodynamic generator accordingto the present invention may be shorter than that of a generator madeaccording to the U.S. Patent No. 3,( )80,515. The reduction of length ofthe conduit and the other advantages of a ionization distributed in asubstantially uniform mannerthroughout the volume owing to the presentinvention are veryimportant from a technical point of view, inparticular the heat losses along the walls are reduced when the lengthof the conduit is shorter.

In a general manner, while we have, in the above description, disclosedwhat we deem to be practical and efficient embodiments of our invention,it should be well understood that we do not wish to be limited theretoas there might be changes made in the arrangement, disposition and formof the parts without departing from the principle of our invention ascomprehended within the scope of the appended claims.

What we claim is:

1'. In a magnetohydrodynamic generator:

an elongated conduit made of an electrically insulating material andadapted to be traversed by a hot gaseous stream containing constituentsionizable in positively and negatively charged fragments;

means for producing inside said conduit a substantially uniform magneticfield substantially perpendicular to the longitudinal direction of saidelongated conduit;

a plurality of pairs of substantially flat collecting electrodes securedagainst the inside wall of said conduit, the two collecting electrodesofeach pair being disposed in a confronting position with the flatsurfaces thereof substantially parallel to the longitudinal direction ofsaid elongated conduit and to said magnetc field, and being connected,outside said conduit, through a utilization load;

a plurality of pairs of substantially elongated ionization electrodescarried by and traversingthe wall of said conduit, and electricallyinsulated from said collecting electrodes, each of said ionizationelectrodes having a discharge end located inside said conduit and a feedend located outside said conduit, the discharge ends of the twoionization electrodes of each pair being disposed in a confrontingposition, with the direction of the straight line connecting saiddischarge ends of the two ionization electrodes being substantiallyperpendicular to the longitudinal direction of said elongated conduit;

and means for applying in operation, between the feed ends of the twoionization electrodes of each pair, voltage pulses having a suflicientamplitude to produce aros between the discharge ends of said twoelectrodes through said gaseous stream flowing in operation through saidconduit in the longitudinal direction thereof. i

2. A magnetohydrodynamic generator as claimed in claim 1, wherein thestraight line connecting the discharge ends of the two ionizationelectrodes of each pair is substantially parallel to said magneticfield.

3. A magnetohydrodynamic generator as claimed in claim 1, wherein saiddischarge ends of said ionization ele c'trodes are substantially flushwith the inside wall of said Conduit. i 1

I References Cited by the'Egeamlner- UNITED STATES PATENTS 2,487332'11/1949 Hagen 313-161 x 3,171,oo 2/1955 wood ez 51. 313. 3x e 3.133,4035/1965; nufwnz 313-231 6 FQREIGN PATENTS 106,899 3`/ 1939 Australia.

JAMES w. LAwRENcE, Pfimary Ex'gzminzr.

GEORGE WESTBY, Examner. S. D. SCHLOSSER, Assistant Exqmiher.

1. IN A MAGNETOHYDYNAMIC GENERATOR; AN ELONGATED CONDUIT MADE OF ANELECTRICALLY INSULATING MATERIAL AND ADAPTED TO BE TRANSVERSED BY A HOTGASEOUS STREAM CONTAINING CONSTITUENTS IONIZABLE IN POSITIVELY ANDNEGATIVELY CHARGED FRAGMENTS; MEANS FOR PRODUCING INSIDE SAID CONDUIT ASUBSTANTIALLY UNIFORM MAGNETIC FIELD SUBSTANTIALLY PERPENDICULAR TO THELONGITUDINAL DIRECTION OF SAID ELONGATED CONDUIT; A PLURALITY OF PAIRSOF SUBSTANTIALLY FLAT COLLECTING ELECTRODES SECURED AGAINST THE INSIDEWALL OF SAID CONDUIT, THE TWO COLLECTING ELECTRODES OF EACH PAIR BEINGDISPOSED IN A CONFRONTING POSITION WITH THE FLAT SURFACES THEREOFSUBSTANTIALLY PARALLEL TO THE LONGITUDINAL DIRECTION OF SAID ELONGATEDCONDUIT AND TO SAID MAGNETIC FIELD, AND BEING CONNECTED, OUTSIDE SAIDCONDUIT, THROUGH A UTILIZATION LOAD; A PLURALITY OF PAIRS OFSUBSTANTIALLY ELONGATED IONIZATION ELECTRODES CARRIED BY AND TRAVERSINGTHE WALL OF SAID CONDUIT, AND ELECTRICALLY INSULATED FROM SAIDCOLLECTING ELECTRODES, EACH OF SAID IONIZATION ELECTRODES HAVING ADISCHARGE END LOCATED INSIDE SAID CONDUIT AND A FEED END LOCATED OUTSIDESAID CONDUIT, THE DISCHARGE ENDS OF THE TWO IONIZATION ELECTRODES OFEACH PAIR BEING DISPOSED IN A CONFRONTING POSITION, WITH THE DIRECTIONOF THE STRAIGHT LINE CONNECTING SAID DISCHARGE ENDS OF TWO IONIZATIONELECTRODES BEING SUBSTANTIALLY PERPENDICULAR TO THE LONGITUDINALDIRECTION OF SAID ELONGATED CONDUIT; AND MEANS FOR APPLYING INOPERATION, BETWEEN THE FEED ENDS OF THE TWO IONIZATION ELECTRODES OFEACH PAIR VOLTAGE PULSES HAVING A SUFFICIENT AMPLITUDE TO PRODUCE ARCSBETWEEN THE DISCHARGE ENDS OF SAID TWO ELECTRODES THROUGH SAID GASEOUSSTREAM FLOWING IN OPERATION THROUGH SAID CONDUIT IN THE LONGITUDINALDIRECTION THEREOF.